1. Field of the Invention
The present invention relates to a semiconductor memory device and a method of manufacturing the semiconductor memory device.
2. Related Art
In recent years, an FBC (Floating Body Cell) memory device is proposed as one of semiconductor memory devices expected as a memory replacing a DRAM (Dynamic Random Access Memory). In the FBC memory device, an FET (Field Effect Transistor) having a floating body (hereinbelow, also simply called body) is formed on an SOI (Silicon On Insulator) substrate, and data “1” or “0” is stored by the number of majority carriers stored in the body. In the case where the FBC is an n-type FET, data is stored by the number of holes in the body.
To improve the retention characteristic of the data in the FBC, there is a case that a plate electrode is provided on a side surface or a bottom surface of the body. By the adequate potential of the plate electrode, the body potential can be stabilized, and the signal difference between data “1” and data “0” and the data retention characteristic can be improved.
As an FD (Fully Depleted) type FBC in which the body is fully depleted, a fin-type FET has been developed. In the Fin-type FET, gate electrodes are provided on both side surfaces of the body, and the both side surfaces of the body are used as channel (multi-channel). With the configuration, the drive current between the source and drain can be increased.
In the case of applying the fin-type to the FBC memory, however, since the fin-type FET has gate electrodes on both side surfaces of the body, the plate electrode cannot be provided on the side surfaces of the body. Although the plate electrode can be provided on the bottom surface of a Fin, the width of the Fin (width between both side surfaces along which channels are formed) has to be narrowed to form an FD type FBC. Therefore, it is difficult to sufficiently assure the capacitance between the plate electrode and the body only by the bottom surface of the Fin.